Radio bomb release system



Aug. 6, 1957 D. BLITZ ET AL RADIO BOMB RELEASE SYSTEM 2 Sheets-Sheet 1Filed July 3, 1945 INVENTOR5 y 01rv1ryfi5c f7 Tram i) 2,802,206 RADIOBOMB RELEASE SYSTEM Daniel Blitz and Irving Wolff, Princeton, N. J.,assiguors, by mesne assignments, to the United States of America asrepresented by the Secretary of the Navy Application July 3, 1945,Serial No. 602,950 Claims. (Cl. 343-7) This invention relates to radiobomb release systems, and more particularly to improvements in systemsof the type described in copending U. S. application Serial No. 524,794,filed on March 2, 1944, by Royden C. Sanders, Jr., and William R.Mercer, and entitled Radio Bomb Release System, which issued December17, 1946, as Patent No. 2,412,632. r

The principal object of the present invention is to pro vide a system ofthe described type including means for automatically compensating theefiects of climbing or diving of the bomber craft so as to providecorrect op eration at any rate of climb or dive within a predeterminedrange.

The invention will be described with reference to the accompanyingdrawings wherein:

Figure 1 is a diagram showing the geometry of a bomb release problem,

Figure 2 is a graph showing the relationship of slant range to slantspeed for bomb release at a particular a1- titude, and the linearapproximation to said relationship,

Figure 3 is a schematic circuit diagram of a radio bomb release systemembodying the present invention,

Figure 4 is a graph illustrating the variations in frequency of thesignals transmitted and received in the operation of the system ofFigure 3, and

Figure 5 is a graph illustrating the variations in frequency of the beatsignal produced in the operation of the system of Figure 3.

The bomb release problem Refer to Figure 1. It is assumed that anaircraft at the point P is flying horizontally at a velocity v toward apoint M, directly over a target at the point Q, at an altitude A. A bombreleased at the altitude A without any vertical velocity will require atime T: to fall to the level of the target.

(1 A 2 and If the horizontal speed V and the horizontal component'd ofthe target range were known, the calculation of T would be a simplematter. The condition for release 1s:

T=Tf, or substituting (2) in (3) nited States Patent Otlice 2,802,206Patented Aug. 6, 1957 Radio reflection equipment does not measure thehorizontal distance d, but the true or slant distance D. Similarly, thehorizontal speed V is not measured, directly, but its slant component vis measured. Accordingly, it is necessary to determine the time T interms of these quantities. It is apparent from Figure 1 that at greatdistances or low altitudes from the target, the target depression angle0: will be small, and the slant speed and slant range will be nearly thesame as the horizontal speed and horizontal range. As the distance isdecreased or the altitude increased, the differences between the slantand horizontal speeds and distances will increase.

Referring to Figure 2, the curve 1 shows the relation between slantspeed v and slant range D which corresponds to one particular value ofT1, which in turn is the time of fall T: from an altitude A1. Thus if abomb is released from the altitude A1, when D and v are of such valuesas to satisfy the relationship represented by the curve 1, the bomb willstrike the target.

For every different altitude, there is a diiferent relationship betweenD and v which must be satisfied for proper release. The curve 1 is thusbut one of a family of similar curves. In the present system a linearapproximation is used, rather than the actual Dv relationship. Thisapproximation need be accurate only within the range 111 to v2 of slantspeeds which will occur in the practical operation of the system. Thedash line 3 in Figure 2 is the linear approximation to the curve 1 whichproduces the smallest maximum error throughout the range of slant speedsfrom 1 1 to 112.

The equation of the line 3 is where m is the slope of the line:

and Do is the range intercept at zero speed, as indicated in Figure 2.As stated above, the relations shown in Figure 2 correspond to onespecified altitude, A1. For any other altitude, both m and D0 will havecorrespondingly different values. By setting in the values of m and Docorresponding to the particular altitude A at which a craft is flying, asubstantially correct release may be obtained by satisfying therelationship of Equation 5.

In the above analysis it has been assumed that the bombing craft is inlevel flight at a constant altitude. Now suppose the altitude ischanging at a rate of climb Y. (If the altitude is decreasing, Y isnegative.) The equation of fall is:

The altitude Ay at which the bomber would have to fly, without climb, tocause the same time of fall as would be caused by flying at the altitudeA with the rate of climb Y, is found by substituting Equation 8 inEquation 1.

For the same time of fall, the diiference between the altitudes whenclimbing and when flying level is 10 A,,A=AA:AA= Y +2g1l For smallvalues of Y and large values of A, AA is approximately:

, Radio and e'or'ripzl'fi system ,iierer is Figure A radio transmitter 5is provided 7 with an antenna 7, and is connected to a frequencymodulator 9, which may be of the type described in coperrding U. .patentapplication Serial No. 471,003, filed January .1, 1943, by S. V. Perry,and entitled Capacity Modulator Unit, now abandoned, or'any other knowndevice for varying the frequency of operation .of the transmitter 5 inaccordance with the voltage applied to it. In the present illustration,the modulator 9 is energized in such manner as to provide triangularwave frequency'rnodula'tion of the transmitter 5. I v v .A.D.-C. source11 is connected across resistors 13, 15 and 17. I adjustable resistor isconnected across the resistor 15.- A switch 19'is connected across theresistor 17, a'ndis arranged to be cyclically opened and "closed by acam 21, continuously driven by a motor 23. This periodic'ally changesthe voltage at thejunction point 14 of resistors 13 and 15 between twovalues which differ by an amount depending upon the setting of theresistor 25. The point 14 is connected to a wave shaping circuit 27. Thecircuit. 27 may be merely an integrating circuit, or

may be of the type described in copending U. S. patent applicationSerial No. 546,537, filed July 25, 1944, by

Royden ,C. Sanders, I12,- and entitled Wave Shaping Cir- ;cuits, whichissued July 9, 1946, as Patent No. 2,403,616. The circuit 27 convertsthe square wave voltage input from the point 14'to a substantiallytriangular Wave voltage, which is applied to the modulator 9. A resistor29 is included in the input circuit of the wave shaping circuit 27. Byadjusting the resistor 25, the band width through which the frequency ofthe transmitter 5 is swept may be varied. I

A receiver 31 is provided with an antenna 33, and is also coupled to thetransmitter 5 through a transmission line 35. An amplitude limiter '37is connected to the output 'of the receiver 31. The output circuit ofthe limiter 37 is connected to a pair of frequency responsive circuitscompr ing su' e'raging cycle counters 39 and 41 respectively. Thecounter39 includes a capacitor 43, connected from -the lim'iter 37 to the anodeof a triode 4s and to the cam ode or a diode 47. The cathode of thetriode 45 is con- "fiecfedfto 'thecon't'rol grid of an amplifier tube49. The

entire load resistance 51 associated with the tube 49 is connected initscathode circuit so that it acts as a so-called cathode follower. 'Theanode of the diode 47 is connected to atap S3 onth'e resistor 5-1.

The counter 41 includes a 'capacitor SLSconnected from the limiter 37 tothe anode of a triode 57 ahdto'th'ecathode of a diode 59.The'anodeof-the diode 59 is connected to the control grid of the cathodefollower tube 49. The cathode of the triode57, is connected to the upperend of the load resistor 51, a't'the cathode of the tube 49. Thecounters 39 and 41 are provided with a common storage 1 control grid ofthe triode 51 is coupled to the same point througha phase'inverte'r "67,so that the square wave voltage applied thereto is 180 outof phase withthat at the grid of the triode 45. The connections are such that thetriode 57 is cut off and the triode 45 is conductive while the frequencyof'th'e' transmitter 5 is increasing, and the triode 45 is cut off andthe triode 57 is conductive while the transmitted frequency isdecreasing. V

The cathode of the 'cathode follower tube 49 is concapacitor 61,'connectedbetwee'n the control grid of the described is as follows:

passed to the cathode through a capacitor 73, and is connectedthrough aresistor to the adjustable contact of a variable voltage divider 77.

The voltage divider, 77 is shunted across a portion of a voltage dividerchain including fixed resistors 79, 81, 83 and 85, and variableresistors 87 and 89, serially connected across the D.-C. source 11. Thevoltages at'the terminals of the voltage divider 77 are controlled bythe variable resistors 87 and 89, and the potential at the control gridof the relay tube 69 is variable between these two voltages byadjustment o'fthe voltage divider 77. The return point 65 of the counterload resistor 63 is the junction betweenthe fixed resistors 83 and 85.

The adjustment and operation of the system thus far Owing to thecyclical operation of the switch 19 by the motor 23, the frequency ofthe output of the transmitter 5 varies cyclically as shown by the solidline 101 of Figure 4. Some o f thisfoutput is transferred directly tothe receiver '31 through the line 35. The greater portion is radiated bythe antenna 7. Some of the radiated energy strikes the selected target(not shown), and is reflected to the antenna 33. I The time required forthetransmitted energy to travel to the target and back to the antenna 33is proportional to the slant range D from the aircraft to the target.The variations in frequency of the received energy are accordinglydelayed with respect to 'those of the transmitted energy. Thevariationof frequency of the received signal "as a function of time,assuming no'relative motion between the aircraft and the target, isshown by the dot line 103. The delay Tris portional to the range D.

Now if the range is decreasing at a rate v, the frequency of thereceived signal will be increased, owing to are mixed and detected inthe receiver 31. The output of the receiver comprises a beat frequencysignal, which has a frequency equalto the difference in the frequenciesof the two signals applied to the receiver. The frequency of this beatsignal varies with time as shown by the solid line graph 106 of Figure5. The mean value of the beat frequency, indicated by the dash line 107in Figure 5,

is directly proportional to the range R, and is equal to:

246 I where f is the modulating frequency in cycles per second, 1% isthe sweep width, or range of variation of the transmitter frequency, inmegacycles per second, and R is the slant rangein feet. Thebeat-frequency varies cyclically above and below its mean value by theamount Fv. During increaseof transmitter frequency the beat frequencyis:

where in is the mean transmitted frequency (see Figure 4) in cycles persecond, v is th'e slant speed in feet per second, and c is the velocityof wave propagation (the veloc- V period, the counter 39 operates toprovide an average currenti in the direction of the solid arrow throughthe load resistor 63. This current is:

where k1 is a constant directly proportional to the capacitance of thecapacitor 43. The counter 41 does not operate.

During descrease of transmited frequency, the triode 45 is cut oif andthe counter 39 does not operate. The triode 57 is conductive, and thecounter 41 provides an average current i in the direction of the dasharrow through the load resistor 63. This current is:

' .fmfs ft! (16) 246 c where k2 is a constant directly proportional tothe capacitance of the capacitor 55. The common load capacitor 61averages the pulsations in the voltage at the control grid of thecathode follower'tube 49, so that the voltage between the cathodefollower grid and ground is where e, is the potential at the point 65and R1. is the resistance of the load resistor 63.

The cathode of the tube 49 is maintained at substantially the samepotential as the control grid as long as the current through theresistor 51 is only the anode current of the tube 49. Thus the potentialat the cathode of the relay tube 69 is the same as that at the grid ofthe tube 49. The potential at the control grid of the relay tube(referred to ground) is the voltage e at the tap of the voltage divider77. Thus the voltage e between the cathode and the control grid of therelay tube is:

m SD 2 1V! 8 Rearrangillg the terms,

at a

R 2 a=ael+z f.(k.u 2 246 v i+a (g--{-) The quantities k1, k2, RL, fm andf are all constants, determined in accordance with designconsiderations. Therefore Equation 19 can be written as:

( s o 1+ 1f 2 The slant range is therefore:

This may be expressed as Equation above,

, D=mv|-Do 6 where and i-i- 'a o 0= Thus by setting the values of 2 K7.and

1+ '3 0 lfs in accordance with the altitude A, the relay can be made tooperate at the proper release time, within the limits of the linearapproximation of the corresponding D-v curve.

It is apparent from Equation 23 that m is inversely proportional to theband width fs. Accordingly, the proper value of m for any particularaltitude A may be obtained by adjustment of the sweep width control 25.Do, as shown by Equation 24, is also inversely proportional to the bandWidth, and is directly proportional to the voltage which must be presentacross the counter load resistor 63 to cause the relay tube 69 toconduct. This voltage is the diiference between the total. bias fromcathode to grid of the relay tube 69, (e -e and the cut off bias e,, andis a function of the settings of the variable resistors 89, 87, and 77,which control the bias e at the grid of the relay tube 69. The variableresistor 89 is employed to control Do in accordance with the altitude.

The variable resistor 77 is provided to allow variation of the bias 2 onthe relay tube for the purpose of obtaining an adjustable range lead, sothat release may be made to occur a certain distance in advance of thetarget. Since the voltage required for a given range lead will vary withaltitude, the variable resistor 87 is included to set the voltage acrossthe resistor 77 as a function of altitude. Thus a given setting of theresistor 77 will provide a given range lead, regardless of the altitude.

The controls 87, 89 and 25 are ganged on a shaft in order that themodulation band width and the bias voltages may be adjustedsimultaneously to correspond with the altitude. None of these quantitiesare linear functions of the altitude. The resistors 87 and 89 aredesigned with resistance-rotation characteristics comprising two linearportions of dilferent slopes to provide approximately the requiredvariations of voltage with rotation of the shaft 110. Practically, theerrors introduced by this arrangement are negligible.

The modulation band width must be held within about one percent of thecorrect value. While this could be achieved with a tapered variableresistor, there would be difficulty in constructing such a device, andit would necessarily be large in order to obtain the required accuracy.On the other hand, it is relatively easy to make a variable resistor ofreasonable size having an accurately linear resistance-rotationcharacteristic. By proper proportioning of the resistors 13, 15, 17 and29, the variable resistor 25 may be made linear and yet provide thecorrect characteristic of band width vs. shaft position.

Altitude servo system The shaft 110 may be set manually to a positioncorresponding to the altitude at which a bombing run is'to be made.However, it is preferable to have the various adjustments madeautomatically, releasing the attention of the pilot to other matters.Accordingly, an altitude responsive servo system is provided forpositioning the shaft 110.

A reversible motor 111 is coupled to the shaft 110,

' source 115.

where K3 is a cons'tant.

"capacitor 1'57 to-a :resistor 159.

and is connected through a double-throw relay 113 to a The actuatingcoil of the relay 113 is connected in the anode circuit of a relayamplifier tube 117, like the relay tube 69. The control grid of the tube117 is coupled to a bias source comprising an adjustable voltage divider119 connected to the output circuit of a D.-C. amplifier 141. This biasis applied to the tube 117 through a resistor 123.

The resistor 123 comprises the load resistor for a counter circuit 125.The counter 1 25 is connected to the output circuit of an amplitudelimiter 127, which in turn is connected to the output circuit of areceiver 129. A transmitter 131, including means for cyclically varyingthe transmitted frequency, is coupled to the receiver 129 and isprovided with an antenna 133. A similar antenna 135 is connected to thereceiver 129.

The counter 1'25, limiter 1'27, receiver 129, and transniitt'e'r "131comprise a radio reflection altimeter, and cooperate in known manner toprovide a voltage across the load resistor 123 bearing a predeterminedrelationship to the altitude H, and in opposing polarity to the biasVoltage provided by the voltage divider 119. When the algebraic sum ofthis voltage and the voltage at the adjustable tap of the voltagedivider 119 is negative with respect to the cut off voltage of the relaytube 117, the relay 113 isdeen'ergized. This connects the motor to thesource 115 in such polarity as to rotate the shaft 110 in the directioncorresponding to increase of altitude. The tap of the voltage divider isrotated to produce more positive bias, until the voltage across thecounter load resi's'tor is neutralized. The relay tube 117 starts toconduct, energizing. the relay 113 and disconnecting the motor 111 fromits source 115.

The relay 113 is provided with a small dead space so that a slightincrease of energization is required to close the upper contacts. Thusif the voltage across the counterload resistor 123 decreases, the relaywill operate 'to its upper position, energizing the motor 111 to rotateV the shaft 110 in the direction corresponding to decrease of altitude.Thus the shaft 110 is maintained substantially continuously at aposition such that the voltage at the tap of the voltage divider 119corresponds to the altitude.

' Rate of climb compensation It "the voltage across "the terminals ofthe voltage divide'r 119 is maintained constant at a predeterminedvalue, "the angular position of the shaft 110 will bear a predeterminedrelationship to the altitude at all. times. In accordance with"the'prese'nt invention however, the shaft 110"i's set off from theposition corresponding to the altitude an amount AA, in accordance withthe rate of A counter circuit 143 isc'oupled to the output circuit'offlie limiter 127. The counter 143'is connected to pro- "vide acrossits 'lo'ad resistor 145a positive voltage which in teases withiherease'of altitude.

circuit of 'the tube '14 includes a 'meter 151 calibrated in 'iinit's'ofaltitude, and two series resistors 153 and 155.

The anode of the discharge diode of the counter 143 is connected 'tothe'j'unction, of the resistors 153 and 155.

The values 'ofthe resistors 153 and 155 are selected so that the voltage"Ea pred'uced at the cathode of the 'tube 149 in response to the beatfrequency output of the limiter 127 is approximately T he cathodeoft-he-tub'e 149 is conne'cted through a The values of these elements areselected with reference to the usual range: of the rate=climb ofthe-bomber craft, so that-corresponding changes ,in, the altitudevoltage Ea will be differentiated with respect totirne, providing, avoltage proportionaLto across the resistor 159.

The input circuit of the D.-C. amplifier 141- is connectd to theresistor 159. The output circuit of the amplifier 141 includes anadjustable voltage divider 161,; conected acrossthe source 11. Theamplifier 141, in addition toamplifying, inverts the polarity of theinput voltage, iQe. a positive input results in an amplified negativeoutput, and vice versa. The voltage divider 1 61fis ad;

justed to provide a constant voltage of for example ap- V proximately150 volts at its tap, so that in the absence of output from the D..-C.amplifier 141, only this voltage will appear across the voltage divider119, and hence the position of the shaft will correspond to the truealtitude A In the, operation of the system, the voltageat the oathode ofthe tube 149 is substantially (26) dt dt IF", E

But

git dt is the rate of climb, Y. Therefore, (27) E,,=K

. w/ This voltage is amplified and reversed in polarity by the amplifier141 and added to that provided by the voltage divider 161. Thus when thecraft is climbing, the voltage across the voltage divider 119 is reducedfrom its normal value by an amount I! where K4 is K3 times the gain ofthe amplifier 141. Similarly, negative climb, or descent, increases thevoltage applied to the voltage divider 119.

The voltage at the tap of the voltage divider 119 is the product of theangular position of the shaft 110 and the total voltage across theterminals of the voltage divider 119. Thus the variation B in theapplied voltage causes the voltage at the tap to vary by an amountproportional to A times B This causes the shaft 110 to rotate from theposition corresponding to the true altitude by an amount substantiallyproportional to E A.

YA 29 E,,A=K4/T =K4Y- /rl By proper adjustment of the gain of theamplifier 141, the value of the constant K4 may be made such that thechange in position of the shaft 110 corresponds to Y /Z AA-a This is thecondition indicated'by Equation 11 for approximate compensation of theeffects of climb upon the time of fall.

Although the invention hasbeen described as embodied in a specific typeof automatic bomb release system, it is equally applicable to any otherbomb release system wherein adjustment is made for the altitude of thebombing craft. The altitude adjustment will be varied from thatcorresponding to the true altitude in accordance with the rate of climb,as in the described system, to provide substantial correction of theefiect of said climb upon the computed time of fall of the bomb.

Thus the invention has been described as an improvement in bomb releasesystems of the type wherein the altitude, distance and speed of a bomberwith respect to a target are determined and the information used automatically to effect release at the proper time. Approximately correctionis made automatically for the eifects of climb or dive upon the release,by altering the altitude response of the system in accordance with therate of change of altitude.

We claim as our invention:

1. In a radio bomb release system including frequency modulatedtransmitter means, a receiver, counter means differentially responsiveto the output of said receiver during increase and decrease respectivelyof the frequency of said transmitter, relay means responsive to theoutput of said counter means to effect release of a bomb upon theattainment of a predetermined magnitude by the output of said countermeans, an altimeter, means responsive to said altimeter to control themodulation band width of said transmitter means, means for applying abias to said relay means, and means responsive to said altimeter tocontrol said bias; means connected to said altimeter and responsivethereto to produce a voltage of a magnitude which is a predeterminedfunction of altitude, means for differentiating said voltage withrespect to time to provide a second voltage of a magnitude which is apredetermined function of rate of climb, and means responsive to saidsecond voltage to bias said means responsive to said altimeter.

2. In combination on an aircraft with an automatic bomb release systemresponsive to target range and speed and altitude information to drop abomb, a system for compensating the effect upon the operation of saidsystem of a vertical component of velocity of said aircraft, includingaltimeter means for providing an electrical output bearing apredetermined relationship to altitude of said craft, means responsiveto said output to adjust said bomb release system in accordance withsaid altitude, means for providing a second electrical output bearing apredetermined relationship to the rate of climb of said craft, and meansresponsive to said second electrical output to alter said adjustment ofsaid bomb release system by an amount corresponding to a change inaltitude.

w AA= wherein A is the altitude of said craft and Y is the rate ofclimb.

3. In a bomb release system including an altitude shaft, an altimeter,and means for setting the position of said shaft in response to saidaltimeter, a system for compensating the effect of rate of climb,comprising means responsive to said altimeter to produce a voltagesubstantially proportional to VAT, wherein A. is the altitude, means fordifferentiating said voltage to provide a second voltage proportional to/2 where Y is the rate of change of altitude, and means responsive tosaid second voltage to bias accordingly said means for setting theposition of said shaft, whereby said altitude shaft is set off from aposition corresponding to the altitude by an amount proportional to 4.In a bomb release system responsive to range, speed and altitudeinformation to effect release of a bomb upon the attainment'of apredetermined relationship between said factors, the method ofcompensating said system for the eflects of a rate of change of saidaltitude information which comprises the steps of converting saidaltitude information to a control force substantially proportional toVX, where A is the altitude, differentiating said converted informationwith respect to time, and supplying said converted and differentiatedinformation to said bomb release system in addition to said altitudeinformation.

5. In a bomb release system responsive to altitude information todetermine time of release of a bomb, a radio altimeter of the frequencymodulation type, means connected to said altimeter and responsivethereto to supply altitude information to said release system, a beatfrequency responsive cycle counter circuit connected to said altimeter,a voltage differentiating circuit connected to said counter circuit, andfurther means responsive to the output of said differentiating circuitto bias said firstmentioned means system, altering the altitudeinformation supplied to said bomb release system by an amount bearing apredetermined relationship to the rate of change of said altitude.

No references cited.

